n = int(input())

ans = 0
for i in range(1, 10**5):
    x = i // 10
    y = 0
    z = i
    while 0 < x:
        y *= 10
        y += x % 10
        z *= 10
        x //= 10
    z += y
    if n < z * (10**9 + 1):
        break
    else:
        ans += 1

for i in range(1, 10**5):
    x = i
    y = 0
    z = i
    while 0 < x:
        y *= 10
        y += x % 10
        z *= 10
        x //= 10
    z += y
    if n < z * (10**9 + 1):
        break
    else:
        ans += 1

print(ans)